Axle driving apparatus

ABSTRACT

An axle driving apparatus consisting of a housing for compactly housing inner portions of axles, a hydrostatic transmission, and a transmitting mechanism for transmitting power to the axles from an output shaft of the hydrostatic transmission. The housing is partitioned by an internal wall into a chamber containing the hydrostatic transmission and a chamber containing the other transmitting mechanisms. The housing is filled with oil in common with both chambers. A trunnion for changing the output rotation of the hydrostatic transmission is disposed in parallel to the axles. A shock absorber is provided to prevent abrupt speed change. A differential locking device is attached to the differential gear to thereby improve the straightforward running capacity of the vehicle.

FIELD OF THE INVENTION

[0001] The present invention relates to an axle driving apparatus forimproving the straightforward running capacity of a vehicle on a muddyroad or the like, and more particularly to an axle driving apparatuswhich is integrally provided with a hydrostatic transmission(hereinafter referred to as the HST); axles; a power transmittingmechanism, which can easily change the speed of the HST; an oilreservoir, which can absorb an increase in the volume of oil due to anincrease in the temperature of the HST; and a differential lockingdevice, all of which are provided in a single housing.

BACKGROUND OF THE INVENTION

[0002] Conventionally, an axle driving apparatus consists of a housingfor an HST, axles and a power transmitting device for interconnectingthe HST and axles. On the center section of the HST is disposed ahydraulic pump, provided with a vertical input shaft, and a hydraulicmotor, provided with a horizontal output shaft. A plurality of pistonsare disposed in the hydraulic pump cylinder block. The heads of thepistons abut against a movable swash plate. Changing the angle of themovable swash plate changes the pump capacity so as to increase ordecrease the number of rotations of the hydraulic motor. The movableswash plate is slanted, thereby enabling the speed of the HST to bechanged by rotatably operating trunnions supported in the housing. Eachtrunnion is disposed on a longitudinally slanted axis of the swashplate, as disclosed in U.S. Pat. No. 5,456,068, for example.

[0003] A speed change controller, such as a pedal or a lever, which isprovided on the vehicle can be operated normally longitudinally thereofso that its motion can be transmitted to a control arm of the axledriving apparatus through a link mechanism, such as a rod, disposedlongitudinally of the vehicle. Hence, it is preferable that the controlarm swing longitudinally around the lateral axis. One conventionalconstruction is provided with a vertical operating shaft, independent ofthe trunnions, where both trunnions and the vertical operating shaftinterlock with each other. The control arm is provided at one end of theoperating shaft so that the control arm swings longitudinally around thevertical axis, and the other end is constructed so that the trunnionprojects at the axial end thereof from the front wall of the housing. Acontrol arm is provided at the axial end so that the control arm swingslaterally around the longitudinal axis. A complex linkage mechanism,with respect to the vertical operating shaft and trunnions, is requiredin the first construction described above, thereby increasing the numberof parts and assembly time, making the axle driving apparatus tooexpensive to produce. The second construction described above requires aseparate link mechanism for converting the longitudinal motion into alateral motion, thereby requiring space to provide two link mechanismsin the vehicle, making it difficult to apply the apparatus to a vehicleof small size and increasing the number of parts required.

[0004] U.S. Pat. Nos. 5,440,951 and 5,515,747 disclose that when the HSTand the mechanism for transmitting power to the axles from the HST arehoused in the same housing, the housing can be filled with oil to beused as both operating oil for the HST and lubricating oil for thetransmitting mechanism. In this case, a foreign object, such as ironpowder, created by the rubbing of the transmitting mechanism may flowtoward the HST. The iron powder or other foreign object is removed by anoil filter so as not to enter into the HST closed fluid circuit.However, the iron powder or the like may encroach on the piston andswash plate and thereby adversely affect them. The housing is integratedin part with the oil reservoir so as to enable the oil volume in thehousing to be adjusted when expanded due to a rise in temperature.However, the greater the quantity of oil, the larger the increase involume. Thus, the housing must be made larger and the reservoirtherefore becomes larger so that the housing itself has to be large insize.

[0005] U.S. Pat. No. 5,094,077 discloses that in order to prevent thespeed change controller equipped on the vehicle from being hastilyoperated by an operator, a shock absorber is provided on the controlarm. The shock absorber should be disposed above the upper wall of thehousing because the control arm is configured to vertically andlongitudinally swing around the axis on the upper wall of the housing.Therefore, space for disposing the shock absorber without interferencewith an input pulley or an enlarged portion of the upper wall of thehousing is required.

[0006] Further, where a differential gear is provided between the leftand right axles, when one axle is idling, a driving force cannot betransmitted to the other axle. Hence, it is desired to provide adifferential locking device on the axle driving apparatus forintegrating the differential locking device with the HST and the axles.

SUMMARY OF THE INVENTION

[0007] The axle driving apparatus of the present invention ispartitioned by an internal wall provided within the housing, into afirst chamber for housing therein the HST and a second chamber forhousing therein axles and a transmitting mechanism which transmits powerfrom an output shaft of the HST to the axles. Both chambers are filledwith common oil. An oil filter is disposed therebetween to allow thechambers to communicate with each other. One chamber communicates withan oil reservoir. Trunnions for the swash plate to change the outputrotation of the HST are supported between the internal wall and a sideplate fixed to the housing. The trunnions are disposed laterally of andin parallel to the axles. One of the trunnions projects outwardly fromthe housing so as to fix an arm. The shock absorber is connectedthereto, thereby preventing hasty speed change. A differential lockingdevice is attached to a differential gear differentially connecting theleft and right axles. During the normal running of the vehicle, thedifferential rotation can be performed. When one axle is idling, bothaxles are adapted to be directly connected to each other.

[0008] These and other objects of the invention will become moreapparent from the detailed description and examples which follow.

BRIEF DESCRIPTION OF THE FIGURES

[0009]FIG. 1 is a plan view of an axle driving apparatus;

[0010]FIG. 2 is a partially sectional plan view of the same in which anupper half housing thereof is removed;

[0011]FIG. 3 is a sectional view looking in the direction of arrows 3-3in FIG. 2;

[0012]FIG. 4 is a sectional view looking in the direction of arrows 4-4in FIG. 2;

[0013]FIG. 5 is a sectional view looking in the direction of arrows 5-5in FIG. 2;

[0014]FIG. 6 is a sectional view looking in the direction of arrows 5-5in FIG. 2;

[0015]FIG. 7 is a sectional view looking in the direction of arrows 7-7in FIG. 2;

[0016]FIG. 8 is an enlarged sectional plan view of a principal portionof the mechanism of a braking device;

[0017]FIG. 9 is an enlarged sectional side view of a principal portionof the same;

[0018]FIG. 10 is a enlarged sectional view of only a part of a principalportion of the same;

[0019]FIG. 11 is a left side view of a center section of the presentinvention;

[0020]FIG. 12 is a plan view of the same;

[0021]FIG. 13 is a sectional view looking in the direction of arrows13-13 in FIG. 11;

[0022]FIG. 14 a sectional view looking in the direction of arrows 14-14in FIG. 11;

[0023]FIG. 15 is a sectional view looking in the direction of arrows15-15 in FIG. 11;

[0024]FIG. 16 is a sectional view looking in the direction of arrows16-16 in FIG. 12;

[0025]FIG. 17 is a sectional view looking in the direction of the arrows17-17 in FIG. 12;

[0026]FIG. 18 is a sectional view looking in the direction of the arrows18-18 in FIG. 12;

[0027]FIG. 19 is a sectional view looking in the direction of the arrows19-19 in FIG. 12;

[0028]FIG. 20 is a sectional view looking in the direction of the arrows20-20 in FIG. 12;

[0029]FIG. 21 is a bottom plan view of the center section from which thecharge pump has been removed;

[0030]FIG. 22 is sectional view of a differential gear and adifferential locking device;

[0031]FIG. 23 is a side view of a slider of the differential lockingdevice;

[0032]FIG. 24 is a side view of a ring gear of the same; and

[0033]FIG. 25 is a perspective exploded view of the differential gear ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] FIGS. 1-7 show the construction of an axle driving apparatus. Thehousing of the axle driving apparatus comprises an upper half housing 1and a lower half housing 2 joined to each other along a horizontal, flatjoint surface along the periphery of the upper and lower half housings1,2. A bearing for a motor shaft 4 is provided on the joint surfaces ofboth upper half housing 1 and lower half housing 2. Bearings for axles 7are shifted upwardly from the joint surface of both upper half housing 1and lower half housing 2 and are disposed in upper half housing 1 torotatably support axles 7. Axles 7 are differentially connected by adifferential gear unit 23 and project laterally outwardly of thehousing.

[0035] The interior of the housing is partitioned by an internal wall 8into a first chamber R1 for housing therein an HST and a second chamberR2 for housing therein a gear-type drive train which transmits power todifferential gear unit 23 from motor shaft 4 to axles 7. First chamberR1 and second chamber R2 are filled with common oil which forms an oilsump. As shown in FIG. 7, an oil feed lid 6 is provided on an upper wallof upper half housing 1 above differential gear unit 23. The housing canbe filled with operating oil through lid 6. As shown in FIG. 6, an oilflow port 75 is provided in the upper portion of upper half housing 1.Upper half housing 1 communicates through a piping 9, of rubber hose orthe like, with the interior of an oil reservoir 10 mounted at apredetermined position on the vehicle, thereby enabling the volume ofoperating oil in oil reservoir 10 to be adjusted.

[0036] As shown in FIG. 6, an oil bore 8 a is open at a predeterminedposition in internal wall 8 which partitions first chamber R1 fromsecond chamber R2. An oil filter 18 covers oil bore 8 a. In thisembodiment, as shown in FIGS. 2 and 6, oil bore 8 a and oil filter 18are disposed on internal wall 8 between the portion containing the HSTand the portion containing the right side axle 7, thereby enabling oilto flow between first chamber R1 and second chamber R2 through oilfilter 18. Accordingly, oil filling the housing can be used as bothoperating oil for the HST and lubricating oil for the gears andbearings. When the oil enters into first chamber R1 from second chamberR2, foreign objects such as iron powder which are harmful to the HST,are filtered by oil filter 18.

[0037] Internal wall 8 is provided within the housing so that firstchamber R1 is disposed in front of axles 7 and to the side of the drivetrain for transmitting power from motor shaft 4 to differential gearunit 23. Internal wall 8, as shown in FIG. 4, comprises (1) an internalwall portion 1 a erected integrally with the upper inner surface ofupper half housing 1 and is positioned at the end surface on the sameplane as the joint surface of the housing parts 1, 2 and (2) an internalwall portion 2 a erected integrally with the inner bottom surface oflower half housing 2 and positioned at the end surface on the same planeas the joint surface of the housing. When both upper half housing 1 andlower half housing 2 are joined together, the end surfaces of bothinternal wall portion 1 a and internal wall portion 2 a join each otherto form internal wall 8, thereby partitioning the interior of thehousing into first chamber R1 and second chamber R2.

[0038] The HST is housed in first chamber R1. The HST comprises ahydraulic pump P, a hydraulic motor M and a center section 5. Centersection 5 is elongated and is longitudinally disposed in first chamberR1. A vertical surface 91 is formed at the front of center section 5 onwhich hydraulic motor M is disposed. A horizontal surface 90 is formedalong the top of center section 5 on which hydraulic pump P is disposed.A pump shaft 3 is substantially vertically disposed on center portion 5and is positioned between motor shaft 4 and axles 7 which extendsubstantially horizontally and in parallel to each other. A pumpmounting surface 40 is formed on horizontal surface 90 of center section5 for hydraulic pump P. A cylinder block 16 is rotatably and slidablydisposed on pump mounting surface 40. Pistons 12 are fitted into aplurality of cylinder bores in cylinder block 16 and are reciprocallymovable by biasing springs. The heads of pistons 12 abut against athrust bearing 11 a held to the movable swash plate 11. At the center ofmovable swash plate 11, an opening 11 b is provided through which pumpshaft 3 perforates. Pump shaft 3, used also as an input shaft, isdisposed on the rotary axis of cylinder block 16 and is fixed thereto asthat pump shaft 3 and cylinder block 16 rotate together. Pump shaft 3projects at the upper axial end thereof outwardly from the upper wall ofupper half housing 1. An input pulley 43 with a cooling fan 44 is fixedto pump shaft 3. Input pulley 43 is given power from a prime mover (notshown) through a belt transmitting mechanism (not shown).

[0039] As seen in FIG. 6, the piston abutting surface of movable swashplate 11 is disposed perpendicular to the rotary axis of cylinder block16. Movable swash plate 11 is shown in the neutral position. Movableswash plate 11 can be tilted from side to side so as to enable thedischarge amount and discharge direction of oil from hydraulic pump P tobe changed. As seen in FIG. 4, for example, movable swash plate 11 isintegrally provided with trunnions 35L and 35R, which project laterallyfrom both sides of swash plate 11 and are disposed in parallel to axles7. Movable swash plate 11, as shown in FIGS. 2 and 4, is slantinglyrotatably supported between the two parallel walls of internal wallportion 1 a in upper half housing 1 and the side wall of the upper halfhousing 1. A recess 1 b is bored in the side surface of internal wallportion 1 a. Recess 16 has an inner diameter about equal to the outerdiameter of a bearing bush fitted on trunnion 35L. As best seen in FIG.4, trunnion 35L is rotatably supported in recess 1 b. In order to borerecess 1 b in internal wall portion 1 a, an opening 1 c is formed in theside wall of upper half housing 1. A machining tool for boring recess 1b is inserted into upper half housing 1 through opening 1 c. A sideplate 15 for closing opening 1 c is detachably fixed onto the outersurface of the side wall of upper half housing 1 through sealing members(not shown). Trunnion 35R extends into a hollow cylindrical portionintegrally formed in side plate 15 so as to be rotatably supportedtherein. Movable swash plate 11 is longitudinally tilted aroundtrunnions 35L and 35R within first chamber R1, enabling the output ofhydraulic pump P to be changed.

[0040] At the outer surface of side plate 15, a plurality of fins 15 a(see FIG. 3) for receiving cooling wind from cooling fan 44 are disposedin the direction of the flow of the cooling wind. Wind blowing acrossfins 15 a lowers the temperature of oil stored in first chamber R1.

[0041] The axial end of trunnion 35R projects outwardly from side plate15. A control arm 38 (discussed below) is fixed onto the axial end andis connected through a link or wire (not shown), to a speed change levermounted at the driver's seat of the vehicle, so as to rotate around thelateral axis of the vehicle body. This simplifies the transmittingmechanism for slantwise control of movable swash plate 11. A neutralreturn coiled spring 31 is fitted onto trunnion 35R in first chamber R1.Both ends of neutral return coiled spring 31 project forwardly betweenan engaging pin 39 and around an eccentric shaft 33 mounted onto theinner surface of side plate 15 (see FIG. 2). Engaging pin 39 projectsfrom an arm 11 d which projects forwardly from movable swash plate 11.

[0042] Accordingly, when control arm 38 is rotated in order to changethe speed of the vehicle, arm 11 d rotates together therewith and oneend of neutral return coiled spring 31 moves away from the other endtoward engaging pin 39. The other end of neutral return coiled spring 31is retained by eccentric shaft 33 so as to apply a biasing force tocontrol arm 38 which tends to return to the neutral position. When theoperating force to the speed change lever is released, the restoringforce created at one end of neutral return coiled spring 31 returnsengaging pin 39 toward eccentric shaft 33 so as to be held in a neutralposition. A portion of eccentric shaft 33 extending outwardly from sideplate 15 is fixed thereto through an adjusting nut 33 a, which can bereleased to properly rotatably shift eccentric shaft 33, therebyshifting arm 11 d around trunnion 35R through neutral return coiledspring 31. This enables movable swash plate 11 to be adjusted to theaccurate neutral position.

[0043] Control arm 38 is fixed to the end of trunnion 35R which extendsoutside of the housing, as shown in FIG. 3. Control arm 38 issubstantially V-shaped, with a first retaining portion 38 a and a secondretaining portion 38 b. First retaining portion 38 a projects upwardlyto connect with a speed changing member such as a lever or pedal (notshown), and with trunnion 35R when the speed change force is applied.Second retaining portion 38 b projects slantwise rearwardly of thevehicle to connect with one end of a movable portion 73 a of a shockabsorber 73. Shock absorber 73 and control arm 38 are formed to straddleright axle 7. The base of a fixed portion 73 b of shock absorber 73 ispivotally supported to a mounting pin 74 b. Mounting Pin 74 b is mountedto the rear end of a support plate 74 fixed through mounting bolts 74 ato the lower surface of a sleeve for right axle 7. Thus, shock absorber73 connects with control arm 38 so as to prevent a rapid speed changeoperation. Further, the operating force of the speed changing member,when released, does not rapidly return swash plate 11 to its neutralposition, due to the spring force of neutral return coiled spring 31.This prevents an abrupt stop of the vehicle caused by the braking actionof the HST.

[0044] Because shock absorber 73 is disposed longitudinally along oneside of the housing, it is not necessary to consider the height of inputpulley 43 or an enlarged portion of the housing. A reasonable connectionand arrangement is provided allowing control arm 38 to be swung along alateral axis of the apparatus.

[0045] Pressure oil from hydraulic pump P is sent to hydraulic motor Mthrough an oil passage in center section 5. Hydraulic motor M, as shownin FIG. 5, is constructed so that a motor mounting surface 41 is formedalong vertical surface 91 of center section 5. A cylinder block 17 isrotatably slidably mounted to motor mounting surface 41. A plurality ofpistons 13 are reciprocally movably inserted into a plurality ofcylinder bores in cylinder block 17 through biasing springs. A thrustbearing, held to a fixed swash plate 37, abuts against the heads ofpistons 13. Fixed swash plate 37 is fixedly positioned between upperhalf housing 1 and lower half housing 2. Motor shaft 4 is disposed onthe rotary axis of cylinder block 17 and is fixed thereto so that motorshaft 4 and cylinder block 17 move together. One end of motor shaft 4 issupported in a shaft bore provided at the center of motor mountingsurface 41 of center section 5. The other end of motor shaft 4perforates through internal wall 8, formed at the joint surface of upperhalf housing 1 and lower half housing 2, so as to enter into secondchamber 2. Motor shaft 4 is rotatably supported by a bearing 76 fittedinto internal wall 8. Bearing 76 includes an oil-tight seal in order topartition first chamber R1 and second chamber R2. In particular, anO-ring 77 is provided on the outer periphery of bearing 76.

[0046] A brake disc 19 is fixed to one axial end of motor shaft 4positioned in second chamber R2. As shown in FIG. 9 a brake pad 98 isfitted into the inner surface of upper half housing 1 positioned at oneside of the upper portion of brake disc 19. At the opposite side ofbrake disc 19, a brake operating shaft 97 is supported which perforatesthe wall of upper half housing 1 from the outside to the inside thereofthrough a support plate 92. Brake pad 98 and the end surface of brakeoperating shaft 97 are opposite to each other. Brake disc 19 issandwiched therebetween. Brake operating shaft 97 is supported inparallel to motor shaft 4. A brake arm 93 is fixed to the end of brakeoperating shaft 97 outside of the housing. A spring 94 is fitted ontobrake operating shaft 97 between brake arm 93 and support plate 92, soas to bias the end surface of brake operating shaft 97 away from brakedisc 19.

[0047] A flange 97 a is formed within the housing at one end of brakeoperating shaft 97. A plurality (four in this embodiment) of groves 97 bare provided at the surface of flange 97 a facing the inner surface ofthe housing. Cam grooves 92 a, each V-shaped in cross-section andarcuate when viewed in plan are provided at the end surface of supportplate 92, opposite to grooves 97 b. As shown in FIG. 10, balls 95 areinterposed between cam grooves 92 a and grooves 97 b. In suchconstruction, when brake arm 93 is rotated, brake operating shaft 97rotates along its longitudinal axis. Balls 95, held by recesses 97 b,slowly ride onto the shallowest portions of cam groove 92 a from thedeepest portions thereof. This causes brake operating shaft 97 toslidably move, due to the thrust generated thereon by balls 95, towardbrake disc 19 thereby sandwiching brake disc 19 between brake pad 98 andthe end surface of brake operating shaft 97 so as to brake motor shaft4. Flanges 92 b, which extend radially and are V-shaped, are integrallyprovided at the outer end of support plate 92 (see FIG. 8). Elongateslots 92 c, which are oval-arcuate shaped are open in flanges 92 baround brake operating shaft 97. Bolts 96 are inserted into elongateslots 92 c, thereby fixing support plate 92 onto the outer surface ofthe side wall of upper half housing 1. Bolts 96 may be unscrewed toproperly rotate flanges 92 b around brake operating shaft 97, therebyenabling balls 95 to adjust the length of time during which balls 95ride on cam groove 97 b.

[0048] Next, explanation will be given on the construction of centersection 5 for loading thereon hydraulic pump P and hydraulic motor M inaccordance with FIGS. 11 through 21. Center section 5 is longitudinallyelongated and is provided at one side thereof with a bolt bore 5 h andat another side thereof with two bolt bores 5 h. Three mounting boltsare inserted into bolt bores 5 h and are used to fix center section 5 tothe inner wall of upper half housing 1 in first chamber R1. At thecenter of pump mounting surface 40 and at the rear and upper surface ofupper half housing 1 is formed a bearing bore for rotatably supportingthe lower end of pump shaft 3. A pair of arcuate ports 40 a and 40 b areopen longitudinally through center section 5 around a bearing bore. Feedor discharge oil is communicated with cylinder block 16 through parts 40a and 40 b. At the center of motor mounting surface 41, verticallydisposed in front of pump mounting surface 40, is bored a bearing borefor rotatably supporting one end of motor shaft 4. A pair of arcuateports 41 a and 41 b are open vertically and around the bearing bore,thereby communicating feed or discharge oil with cylinder block 17.

[0049] In order to connect arcuate ports 40 a and 40 b at pump mountingsurface 40 with arcuate ports 41 a and 41 b at motor mounting surface41, a first linear oil passage 5 a and a second linear oil passage 5 bare bored in a thick portion of center section 5, in parallel to eachother. As shown in FIG. 12, the center of pump mounting surface 40 ispositioned along an imaginary vertical plane (line 16-16) disposed alongmotor mounting surface 41. Half of cylinder block 16 mounted on pumpmounting surface 40 (as shown in FIG. 2) overlaps, when viewed fromabove, with half of cylinder block 17 disposed on motor mounting surface41. This arrangement permits the HST and first chamber R1 which containsthe HST to be smaller in lateral width. A third linear oil passage 5 ccommunicates horizontally and perpendicularly with an intermediateportion of second oil passage 5 b. Arcuate port 40 a at pump mountingsurface 40, as shown in FIG. 18, is shallow and directly communicateswith first oil passage 5 a. Arcuate port 40 b is deeper to communicatewith third oil passage 5 c. Arcuate port 41 a at motor mounting surface41 is deeper at the upper portion thereof to communicate with first oilpassage 5 a and shallow at the lower portion thereof, as shown in FIGS.16 and 17. Arcuate port 41 b communicates, at the lower portion thereof,with second oil passage 5 b. Thus, first oil passage 5 a communicateswith arcuate port 40 a and with arcuate port 41 a, while second oilpassage 5 b and third oil passage 5 c communicate with arcuate port 40 band with arcuate port 41 b, so as to form a closed fluid circuit incenter section 5.

[0050] With reference to FIG. 17, check valves 54 and 55 are disposed atthe open ends of first oil passage 5 a and second oil passage 5 brespectively. Both first oil passage 5 a and second oil passage 5 b areclosed by plug members 64 a in which check valves 54 and 55 aredisposed, respectively. The open end of third oil passage 5 c is closedby a plug member 64 b. Check valves 54 and 55 communicate at the inletsides thereof with oil passage 5 d through oil bores 54 b and 55 bprovided at casings 54 a and 55 a. The open end of oil passage 5 d ispositioned in a recess 5 g formed at the lower surface of center section5. At the lower surface of center section 5, opposite to pump mountingsurface 40, a charge pump casing 46 is mounted through a plurality ofmounting bolts 69. A trochoid-type charge pump 45 is housed (see FIG. 4)in a recess formed at a center of the upper surface of charge pumpcasing 46. Trochoid-type charge pump 45 is provided with internal teethand external teeth. The lower end of pump shaft 3 projects downwardlyfrom center section 5 and engages with the external teeth so as to drivecharge pump 45. Charge pump 45, however, may be of an external gear typeor other known type.

[0051] As seen in FIGS. 18 and 19, charge pump 45 has a discharge port45 a and an intake port 45 b. Intake port 45 b communicates with anopening 46 b (FIG. 17) into which the open end of a cylindrical oilfilter 56 is inserted (see FIGS. 5 and 6). Oil filter 56 is disposedunder hydraulic motor M in first chamber R1. Oil filter 56 is insertableinto charge pump casing 46 which is in the housing from the exteriorthereof through an insertion bore open at the front wall of lower halfhousing 2. Oil filter 56 is interposed between charge pump casing 46 anda plug member 48 which closes the insertion bore at the front wall oflower half housing 2. Plug member 48 can be removed to facilitatemaintenance and inspection of oil filter 56. A pair of oil joints 49 and50 project from the a side surface of charge pump casing 46 (FIG. 13).The ends of joints 49 and 50, as shown in FIG. 3, are exposed at a lowerportion of the outside surface of lower half housing 2. Oil joints 49and 50 function as an oil pressure source for hydraulic actuatorsequipped outside of the vehicle.

[0052] Oil joint 50 is formed to serve as an oil takeout port andcommunicates with discharge port 45 a of charge pump 45 through an oilpassage 46 a as shown in FIG. 13. A first relief valve 57, for settingthe oil pressure of discharge port 45 a, is housed in charge pump casing46 and is connected to an oil passage 46 c which is branched from oilpassage 46 a. Relief oil discharged from first relief valve 57 flowsinto recess 5 g at the lower surface of center section 5 through oilpassage 46 c. Oil joint 49 is formed to be an oil return port and tocommunicate with recess 59 of center section 5 through oil passages 46 dand 46 e. A second relief valve 58 for setting the oil pressure inrecess 5 g to be supplied to the closed circuit of the HST is housed incharge pump casing 46 and connects with recess 5 g through an oilpassage 46 f. Relief oil discharged from second relief valve 58 isdischarged outwardly from charge pump casing 46 through an oil passage46 g.

[0053] As seen in FIG. 17, when charge pump 45 is driven, oil flowinginto recess 5 g through the oil passage 46 c is adjusted by secondrelief valve 58. This causes check valve 54 or 55 to open through oilpassage 5 d at the low pressure side of one of oil passages 5 a, 5 b or5 c, thereby forcibly supplying operating oil into the closed fluidcircuit for the HST.

[0054] When the vehicle is stopped on a sloping surface, and the HST isput in the neutral position without the parking brake exerted, the forcecausing the driving wheels of the vehicle to roll acts on the closedfluid circuit of the HST to generate pressure so as to cause negativepressure in the closed fluid circuit and possibly causing the vehicle tomove. In order to prevent such a phenomenon, a check valve 47 (see FIG.15) is housed in charge pump casing 46 which can supply operating oil tothe closed fluid circuit of the HST even when charge pump 45 is notdriven. Check valve 47 communicates at the inlet side thereof withintake port 45 b through an oil passage 46 h and at the outlet side withrecess 5 g through an oil passage 46 i. When charge pump 45 is driven toflow operating oil into recess 5 g though oil passages 46 c and 46 e,check valve 47 closes between oil passage 46 h and oil passage 46 i.When charge pump 45 is not driven, causing negative pressure on the lowpressure side of the closed circuit, check valve 47 is open to enableoil filtered by filter 56 to be guided from intake port 45 b and oilpassages 46 h and 46 i into recess 5 g. Check valve 54 or 55, at thenegative pressure side of the closed fluid circuit, is open through oilpassage 5 d, whereby oil is supplied to the closed fluid circuit. Thus,oil can be maintained in the closed fluid circuit at all times.

[0055] In order to place operating oil into the closed fluid circuitafter the axle driving apparatus is assembled, oiling pipes 52 and 53are disposed at the lower surface of center section 5 as shown in FIGS.11, 15, 17 and 20. At the lower surface of center section 5, a fourthvertical passage 5 e is bored to communicate with the upper deep portionof arcuate port 41 a. A fifth vertical oil passage 5 f is bored tocommunicate with second oil passage 5 b. Oiling pipes 52 and 53 aremounted into oil passages 5 e and 5 f respectively and are opened at thelower ends thereof outwardly from the bottom wall of lower half housing2 and closed at the open ends by use of plug members after the closedfluid circuit is filled with operating oil.

[0056] As shown in FIGS. 2 and 5, a by-pass arm 60 for opening theinterior of the closed circuit to the oil sump, in order to enable theaxle to be idle during hauling of the vehicle, is disposed in the upperportion of upper half housing 1. In particular, by-pass arm 60 is fixedat its base onto the upper end of a by-pass shaft 61, which isvertically, rotatably and pivotally supported to the upper wall of upperhalf housing 1. By-pass shaft 61 extends at its lower end into a thickportion of motor mounting portion 41 of center section 5. A flat surface61 a is formed at a part of the outer periphery of the lower end ofby-pass shaft 61. A through-bore 5 i (see FIG. 11) is open at motormounting surface 41 of center section 5 slightly above the centerthereof and between arcuate port 41 a and 41 b. A push pin 62 (see FIG.5) is slidably supported into through-bore 5 i along the rotary axis ofcylinder block 17. One end surface of push pin 62 can abut against therotary sliding surface of cylinder block 17 in close contact with themotor mounting surface 41. The other end surface abuts against flatsurface 61 a of by-pass shaft 61.

[0057] Thus, when an operator operates a by-pass operating lever (notshown) equipped on the vehicle when the vehicle is hauled, by-pass shaft61 is rotated through by-pass arm 60. Push pin 62 is pushed towardcylinder block 17 by the flat surface of the lower end of by-pass shaft61. Push pin 62 moves the cylinder block 17 above motor mounting surface41. First oil passage 5 a and second oil passage 5 b communicate withthe oil sump of the housing through arcuate ports 41 a and 41 brespectively, thereby enabling motor shaft 4 to freely rotate.

[0058] As shown in FIGS. 2 and 7, the drive train for transmitting powerfrom motor shaft 4 to differential gear 23 is constructed with a gear 25provided on a portion of motor shaft 4 entering into second chamber R2,for engaging with a larger diameter gear 24, fixed onto a counter shaft26. A smaller diameter gear 21 is also fixed onto counter shaft 26 andengages with an input gear 22. Power from motor shaft 4 is reduced inspeed by gears 25, 24 and 21 to drive differential gear unit 23 by inputgear 22. Larger diameter gear 24, on counter shaft 26, is disposed tothe side of input gear 22 and overlaps in part therewith. Counter shaft26 is rotatably housed in lower half housing 2 and is supported at bothaxial ends in a recess formed on the side wall of lower half housing 2and a recess formed on the internal wall 2 a of lower half housing 2, asshown in FIG. 2, so as to be rotatably supported when lower half housing2 is joined with upper half housing 1.

[0059] As best seen in FIGS. 2 and 22, the distal ends of axles 7 arerotatably supported by ball bearings in axle housing portions projectingfrom upper half housing 1. The proximate end of each axles 7 is sleevedby a bearing bush. One half of each bearing bush is received in a recessin upper half housing 1. The other half is received by a projection oflower half housing 2 which enters into upper half housing 1. Axles 7 arerotatably supported to receive power transmitted through differentialgear 23. As shown in FIG. 2, the HST is disposed to the right side ofthe drive train. A control arm 38 for movable swash plate 11 is disposedto the right side of the HST. Hydraulic pump P is positionedsubstantially at the lateral and longitudinal center of the apparatusand is disposed so as to avoid the enlarged portion of differential gear23. This enables the housing to be compact.

[0060] Differential gear unit 23 is shown in FIGS. 22 through 25. Asseen in FIG. 24, the center of input gear 22 has a shaft bore 22 a forreceiving axles 7 therein. Bores 22 b for receiving differential pinions80 and fitting-in bores 22 a for receiving the differential lockingdevice are disposed at both sides of input gear 22. Spline-fittedbevel-type output gears 81L and 81R are disposed at the proximate end ofaxles 7. Spindles 80 a of the bevel-type differential pinions 80 areretained in bores 22 b of input gear 22 in which differential pinions 80are also housed. Differential pinions 80 engage with output gears 81Land 81R so as to form differential gear unit 23. No differential casingis otherwise provided. The differential locking device is providedopposite to the drive train at one side (preferably the right side) ofdifferential gear 23 unit.

[0061] Between output gear 81R and the proximate end of right axle 7 isinterposed a collar 83 on which a slider 82 is axially slidably fitted.Slider 82 is cup-like shaped to wrap around output gear 81R. At theouter peripheral side surface of slider 82, projections 82 a areintegrally provided. Projections 82 a are permanently engageable withinsertion bores 22 c of input gear 22. At the inner peripheral sidesurface of slider 82 are formed a plurality of projections 82 b whichare engageable with a plurality of recesses 81 a formed in the outerperiphery of output gear 81R. An insertion groove 82 c is formed on thecylindrical portion of slider 82 opposite to projections 82 a, so as tofit the tip of a fork 84 into groove 82. The base of fork 84 is slidablyfitted onto a shaft 85 which is journalled to both side walls in lowerhalf housing 2. At the side surface of the base of fork 84 is formed acam surface 84 a, which abuts against a pin 87 provided on shaft 85 soas to constitute a cam mechanism. An arm 86 is fixed to shaft 85. Arm 86projects outwardly from the housing so as to connect with a differentiallocking pedal (not shown) provided on the vehicle.

[0062] In such construction, when the operator presses the differentiallocking pedal, shaft 85 rotates through arm 86, and pin 87 rotates topush to the right in the drawing of FIG. 22. As a result, cam surface 84a abuts against pin 87 so as to slidably move fork 84. At the same time,slider 82 slides, while maintaining projections 82 a in insertion bores22 c of ring gear 22. Projections 82 b engage with recesses 81 a ofoutput gear 81R and input gear 22 is differentially locked and coupledwith axles 7. As a result, axles 7 are uniformly driven when the vehicleruns on any road surface.

[0063] The axle driving apparatus of the present invention can be usedfor driving the axles of a vehicle to improve the operability ofchanging the speed of the vehicle. An example of a moving vehicle whichmay utilize the above-mentioned axle driving apparatus is a farm orother working vehicle, such as a tractor with a mower attachment, orother vehicle for transportation.

[0064] While one embodiment of the present invention has been shown anddescribed, the invention should not be limited to the specificconstruction thereof, and is meant to be merely exemplary.

What is claimed is:
 1. An axle driving apparatus for a vehicle,comprising: a housing; an axle disposed in said housing; an input meansdisposed in said housing; a hydraulic pump driven by said input means,wherein said hydraulic pump is provided with a reciprocally movablecylinder block with a plurality of pistons disposed in said cylinderblock, said cylinder block having a rotary axis which is substantiallyperpendicular to a rotary axis of said axle; a movable swash plate forreceiving thrust from the heads of said pistons; means disposed onopposite sides of said movable swash plate in said housing for rotatablysupporting said movable swash plate and for permitting said movableswash plate to slant along an axis substantially parallel to said axle;a hydraulic motor driven by pressurized oil from said hydraulic pump; anoutput means driven by said hydraulic motor; and a drive train fordrivingly connecting said output means and said axles.
 2. An axledriving apparatus for a vehicle according to claim 1 , wherein saidhousing is provided with a first housing member and a second housingmember joined along a plane substantially perpendicular to said rotaryaxis of said cylinder block, and wherein said movable swash plate isslantingly movably housed in said first housing member.
 3. An axledriving apparatus for a vehicle according to claim 2 , wherein saidmeans for rotatably supporting said movable swash plate comprises: afirst trunnion provided at one side of said swash plate having an axiswhich is coincident with a slantingly rotary axis of said swash plateand extends outwardly from one side-wall of said first housing member;and an arm fixed to the outer end of said first trunnion connected witha speed change operating member provided on said vehicle whichlongitudinally swingably moves around said slantingly rotary axis.
 4. Anaxle driving apparatus for a vehicle according to claim 3 , furthercomprising: a shock absorber mounted between said arm and said housingfor applying operational resistance to said speed change operatingmember.
 5. An axle driving apparatus for a vehicle according to claim 3, further comprising; a side plate mounted on one side wall of saidfirst housing member for supporting said first trunnion; and a biasmechanism disposed between said side plate and said movable swash platefor returning said movable swash plate to a neutral position.
 6. An axledriving apparatus for a vehicle according to claim 5 , furthercomprising: a cooling fan disposed above said first housing member andintegrally rotatable with said input means; and a plurality of finsprovided at an outer surface of said side plate and disposed in thedirection of the flow of cooling wind generated by said cooling fan. 7.An axle driving apparatus for a vehicle comprising: a housing; ahydrostatic transmission disposed in said housing, including an inputmeans, a hydraulic pump driven by said input means, a hydraulic motordriven by pressurized oil from said hydraulic pump, and an output meansdriven by said hydraulic motor; an axle; and a drive train forconnecting in a driving manner said output means of said hydrostatictransmission with said axle; wherein said hydraulic pump is providedwith a reciprocally movable cylinder block, containing therein aplurality of pistons and having a rotary axis substantiallyperpendicular to a rotary axis of said axles, a movable swash plate forreceiving thrust from the heads of said pistons, and a means forslantingly rotatably supporting said movable swash plate in saidhousing; wherein said means for slantingly rotatably supporting saidmovable swash plate includes a first trunnion and a second trunnionprovided at lateral sides of said movable swash plate and disposed onthe same axis and in substantially parallel to said axle, two wallportions provided in said housing and disposed opposite to each otherand extending longitudinally of said axle and a first bearing and asecond bearing provided at said two wall portions for receiving saidfirst and second trunnions, respectively.
 8. An axle driving apparatusfor a vehicle according to claim 7 , wherein said housing is providedwith at least a first hosing member and a second housing member joinedalong a plane substantially perpendicular with respect to the rotaryaxis of said cylinder block, said first housing member being providedwith said two wall portions for supporting said movable swash plate. 9.An axle driving apparatus for a vehicle according to claim 8 , wherein aside wall of said first housing member forms one of said two wallportions, said first trunnion in part extends outwardly from said sidewall of said first housing member and an arm is fixed to said trunnionin part, said arm longitudinally swinging around said first trunnion andconnected with a speed changing member equipped on said vehicle.
 10. Anaxle driving apparatus for a vehicle according to claim 9 , furthercomprising: an opening provided at said side wall of said first housingmember; and a side plate mounted on said side wall of said first housingmember for closing said opening; wherein said first bearing is providedin said side plate.
 11. An axle driving apparatus for a vehicleaccording to claim 9 , further comprising: an other side wall of saidfirst housing member opposite said side wall of said first housingmember; a first internal wall potion provided between said side wall ofsaid first housing member and said other side wall of said first housingmember; wherein one of said two wall portions is constructed at said oneside wall of said first housing member and the other of said two wallportions is constructed at said first internal wall portion.
 12. An axledriving apparatus for a vehicle according to claim 11 , furthercomprising: a side wall of said second housing member; an other sidewall of said second housing member; a second internal wall portionprovided between said side wall of said second housing member and saidother side wall of said second housing member, wherein end surfaces ofsaid first internal wall portion and said second internal wall portionextend toward said plane, overlapping each other when said first housingmember and said second housing member are joined and forming in saidhousing a first section for containing therein said hydrostatictransmission and a second section for containing therein said drivetrain.
 13. An axle driving apparatus for a vehicle according to claim 12, further comprising: an intermediate transmitting member disposedbetween said output means and said axles, said intermediate transmittingmember having a rotary axis extending substantially in parallel to saidplane; and a shaft for disposing thereon said intermediate transmittingmember, said shaft being sandwiched between said first internal wallportion and said second internal wall portion for support.
 14. An axledriving apparatus for a vehicle comprising: a housing; a hydrostatictransmission disposed in said housing including an input means, ahydraulic pump driven by said input means, a hydraulic motor driven bypressurized oil from said hydraulic pump, and an output means driven bysaid hydraulic motor; an axle; a drive train for connecting in a drivingmanner said output means of said hydrostatic transmission and said axle;an internal wall provided in said housing which separates the interiorof said housing into a first chamber, containing therein saidhydrostatic transmission and for storing operating oil for saidhydrostatic transmission, and a second chamber, containing therein saiddrive train and for storing oil for lubricating said drive train; an oilbore open at said internal wall; and an oil filter for covering said oilbore, wherein said oil freely communicates between said first chamberand said second chamber through said oil filter.
 15. An axle drivingapparatus for a vehicle according to claim 14 , further comprising: afirst housing member and a second housing member joined on a planesubstantially in parallel to said axles, a first internal wall portionprovided in said first housing member; and a second internal wallportion provided in said second housing member; wherein said firstinternal wall portion and said second internal wall portion extend atthe end surfaces thereof toward said plane and join each other when saidfirst housing member and said second housing member are joined, therebyforming said internal wall.
 16. An axle driving apparatus for a vehicleaccording to claim 14 , further comprising: an outside reservoir fluidlyconnected to said first chamber for adjusting a change in volume of saidoil stored in said first chamber for said hydrostatic transmission. 17.An axle driving apparatus for a vehicle according to claim 14 , furthercomprising: a charge pump for supplying operating oil circulatingbetween said hydraulic pump and said hydraulic motor and driven by saidinput means; and a second oil filter connected to a suction side of saidcharge pump for filtering said oil in said first chamber and for guidingsaid oil to the suction side of said charge pump.
 18. An axle drivingapparatus for a vehicle according to claim 14 , further comprising;hydraulically operated instruments provided outside said housing; an oiltakeout pump driven by said input means for supplying said oil in saidhousing to said hydraulically operated instruments; and a second oilfilter connected to a suction side of said oil takeout pump forfiltering said oil in said first chamber and for guiding said oil tosaid suction side of said oil takeout pump.
 19. An axle drivingapparatus for a vehicle comprising: a housing; a hydrostatictransmission disposed in said housing, including an input means, avariable displacement type hydraulic pump of driven by said input means,a hydraulic motor driven by pressurized oil from said hydraulic pump,and an output means driven by said hydraulic motor; an axle; a drivetrain for drivingly connecting said output means of said hydrostatictransmission with said axle; a control shaft for changing the volume ofsaid hydraulic pump, said control shaft extending substantially inparallel with respect to said axles and positioned at one side of saidhousing; an arm fixed to said control shaft, positioned on one side wallof said housing, and longitudinally swinging around said control shaftconnecting with a speed change operating member provided on saidvehicle; and a shock absorber for applying operational resistance tosaid speed change operating member, said shock absorber having a movableportion and a fixed portion, one of said movable portion and said fixedportion is mounted to said housing while the other is mounted to saidarm.
 20. An axle driving apparatus for a vehicle according to claim 19 ,wherein said housing is provided with a first housing member and asecond housing member joined on a plane substantially in parallel withrespect to said rotary axis of said axle, said control shaft projectingoutwardly from said one side wall so that said arm is mounted to saidcontrol shaft.
 21. An axle driving apparatus for a vehicle according toclaim 20 , wherein said axle being rotatably supported in said firsthousing member and the ends of said axle outwardly project from oppositeside wall of said housing.
 22. An axle driving apparatus for a vehicleaccording to claim 19 , further comprising: a first mounting portionprovided on said arm for said shock absorber; and a second mountingportion for said shock absorber provided at a position opposite to saidcontrol shaft across from said axle, wherein said shock absorber ismounted to a fixed portion and to a movable portion thereof in thevicinity of said axle.
 23. An axle driving apparatus for a vehicleaccording to claim 22 , wherein said housing is provided with at a firsthousing member and a second housing member joined on a planesubstantially in parallel with respect to the rotary axis of said axle,said first mounting portion being positioned at a side of said firsthousing member, said second mounting portion being positioned at a sideof said second housing member, said shock absorber being mounted at afixed portion and a movable portion thereof to said first and secondmounting portions respectively, intersecting said plane.
 24. An axledriving apparatus for a vehicle comprising: a housing; a hydrostatictransmission disposed in said housing, including a substantiallyperpendicular input means, a hydraulic pump of variable displacementtype driven by said input means, a hydraulic motor driven by pressurizedoil from said hydraulic pump, and horizontal output means driven by saidhydraulic motor; a differential gear means including an input gear, afirst output gear and a second output gear in said housing; a first axleand a second axle driven by said first output gear and said secondoutput gear, respectively; and a drive train for drivingly connectingsaid output means of said hydrostatic transmission and said input gearof said differential gear means; wherein said differential gear means isprovided with a clutch means for freely connecting said input gear tosaid first axle.
 25. An axle driving apparatus for a vehicle accordingto claim 24 , wherein said housing is provided with a first housingmember and a second housing member joined on a plane substantially inparallel with respect to the rotary axes of said first axle and saidsecond axle, said housing including support means for supporting saidfirst axle at the base thereof; wherein said clutch means includes aclutch slider disposed between said first output gear and said supportmeans and is slidable longitudinally of said first axle.
 26. An axledriving apparatus for a vehicle according to claim 25 , wherein saidclutch slider is provided with a first engaging unit permanentlyengageable with said input gear and a second engaging unit detachablyengageable with said first output gear.
 27. An axle driving apparatusfor a vehicle according to claim 26 , wherein said clutch meanscomprises; an operating shaft substantially in parallel to said firstand second axles; a fork member slidably disposed at the outer peripheryof said operating shaft and engageable with said clutch slider; an armdisposed at one side of said housing and connected with one end of saidoperating shaft; and a cam means for converting rotating motion of saidoperating shaft into linear motion so as to be transmitted to said forkmember when said arm is moved in a swinging motion around said operatingshaft.